1. Field of the Invention
The present invention relates to an image display apparatus. The image display apparatus according to the present invention is suitable for a head-mount display (HMD) and a spectacle-type display, for example.
2. Description of the Related Art
Various head-mounted image observer systems (image display apparatuses) in that images displayed on an image display panel, such as a liquid crystal display panel, are observed as enlarged virtual images, so-called head-mount displays (HMDs), have been proposed.
Among them, an HMD including a reflective liquid crystal panel has been known (Japanese Patent Laid-Open No. H11-125791 (corresponding to U.S. Pat. No. 6,333,820), No. H11-337863 (corresponding to U.S. Pat. No. 6,023,373), No. 2000-010041, and No. 2002-244076 (corresponding to U.S. Pat. No. 7,081,999)).
In the HMD including a reflective liquid crystal panel, an observational light beam proceeds to an illumination light source, an illumination optical system, the reflective liquid crystal panel, a display optical system, and eyeballs, in that order.
Japanese Patent Laid-Open No. H11-125791, No. H11-337863, and No. 2000-010041 disclose an HMD having a free-form surface prism and the reflective liquid crystal panel combined with each other.
Japanese Patent Laid-Open No. 2002-244076 discloses an HMD including the reflective liquid crystal panel and a cylindrical curved surface as the illumination optical system for miniaturizing the entire apparatus so that the illuminance is increased by condensing the light from the light source with the cylindrical curved surface.
When the reflective liquid crystal panel is used as an image display apparatus, in order to miniaturize the entire apparatus, it is especially important to appropriately configure an illumination device for illuminating the liquid crystal display panel.
In order to achieve a small-sized illumination optical system, in Japanese Patent Laid-Open No. 2002-244076, for example, a half-mirror is included in the illumination optical system so that the illumination light is led to the reflective liquid crystal panel. Since the liquid crystal panel is a modulating device employing polarization, a metal with small difference in polarization characteristics, such as aluminum, is used for the half-mirror.
However, in the half-mirror made of aluminum, when the incident angle of light on the half-mirror surface is changed, the light availability is largely reduced.
Reduction in light availability requires the illumination light source to be further illuminative, so that the electric power availability is reduced, increasing the heat emission of the HMD itself.
Accordingly, in the image display apparatus employing the liquid crystal panel, it is important to appropriately configure the light source and the illumination optical system ranging from the light source to the liquid crystal panel.